1. IR absorption Greenhouse gases vary in their ability to trap IR radiation, One molecule of Methane is 26 times more effective at IR absorption than one molecule of CO 2.

2. Lifetime Effectiveness also depends on the lifetime in the atmosphere. Methane remains in the atmosphere for about a decade, CO 2 has an effective lifetime of ~1000 years.

3. Global warming potential (GWP). The effectiveness of a greenhouse gas relative to CO 2 is its global warming potential (GWP).

4. GWP on a per kilogram basis